*Goku arrives on namek* "Ah...now it's so peaceful!"
*Krillin in distance* "HELP! WE'RE GONNA DIE! HEEELLLP!"
Goku: "That sounds like a duck! That's silly!"
Krillin: "Quack....quack..."
Goku: *gasp* "That sounds like Krillin! Hold on!!"
So to answer your question, ducks don't quack, Krillin does.